A film scanner typically includes a linear CCD array image sensor which provides a serial output of signals representing successive lines of an image. For color applications, the film scanner may include an assembly of three separate linear CCD array image sensors, or a tri-linear CCD array, one for each of the primary colors. The film is driven at a uniform rate past a linear light beam provided by an illumination system which illuminates a line section or stripe of the film. A scan line of the illuminated stripe is imaged onto each of the tri-linear CCD array image sensors. The film motion provides the frame scan, and the linear cycling of the CCD elements provides the line scan for each color. Film scanners of this type are disclosed, for example, in U.S. Pat. No. 4,868,383 and in the above-referenced '197 and '661 applications.
As shown in these applications and the '383 patent, it is common for film scanners to have an illumination system which produces a line or strip of light across the film that is imaged on the linear CCD array image sensor. The lamps used in such systems normally produce a circularly symmetric light beam, and there is a problem that is addressed with varying degrees of success in these systems in providing for an efficient conversion of the circular beam into a line of uniform intensity sufficient to provide a high signal to the CCD elements. In addition, it is the purpose of these systems to suppress the effects of film surface defects or artifacts by close positioning of the film plane with the light exit slit or aperture and by controlling the angular diffusion of the line of light. The uniform line of diffuse light suppresses film scratches which would otherwise appear in an image produced from the scanned information.
In the film scanners disclosed in the '383 patent and the above-referenced '197 and '661 applications, the linear light source for the film scanner includes the lamp for generating an intense beam of light, a set of filters for filtering the light beam, and an elongated cylindrical integrating cavity having diffusely reflective walls. The intense light beam is introduced into the integrating cavity through an input port and exits through a light exit slit or aperture which extends parallel to the longitudinal axis of the cylindrical integrating cavity.
In the '383 patent, the input port (or ports, when two lamps are used) is located in an end wall or the side wall of the cavity out of direct line of sight of the aperture to avoid the direct transmission of the incoming light beam out through the exit aperture, which can cause an undesirable effect. In commonly assigned U.S. Pat. No. 5,215,370, elongated plates are aligned with the exit aperture extending along and either inside or outside the cavity thereby reducing flare.
In commonly assigned U.S. Pat. No. 5,103,385 and in the above-referenced '197 application, for example, the light input port in the side wall is oriented directly across from the output aperture, and an axially extending baffle blocks the direct transmission of the incoming light beam out through the aperture. The centrally disposed baffle may be either rectangular or circular or otherwise shaped in cross-section, as long as the width or diameter is large enough to block the direct light transmission.
In each case, the incoming light is reflected off the surfaces inside the light integrating cavity one or more times before exiting through the aperture. Such linear light integrators produce a line of diffuse light which has a nearly uniform linear intensity and angularly diffuse distribution, and excellent results can be obtained over a wide range of operating conditions.